Low Temperature Co-fired Ceramics Tapes Research Articles

Laser Ablation of Thin Films on LTCC

Direct Digital Manufacturing techniques such as laser ablation are proposed for the fabrication of lower cost, miniaturized, and lightweight integrated assemblies with high performance requirements. This paper investigates the laser ablation of a Ti/Cu/Pt/Au thin film metal stack on fired low temperature cofired ceramic (LTCC) surfaces using a 355 nm Nd:YAG diode pumped laser ablation system. It further investigates laser ablation applications using unfired, or ‘green’, LTCC materials: (1) through one layer of a laminated stack of unfired LTCC tape to a buried thick film conductor ground plane, and (2) in unfired Au thick films. The UV laser power profile and part fixturing were optimized to address defects such as LTCC microcracking, thin film adhesion failures, and redeposition of Cu and Pt. An alternate design approach to minimize ablation time was tested for efficiency in manufacture. Multichip Modules (MCM) were tested for solderability, solder leach resistance, and wire bondability. Scanning electron microscopy (SEM) as well as cross sections and microanalytical techniques were used in this study.

Determination of LTCC Shrinkage Variations from Tape Manufacturer to Consumer

Low Temperature Cofired Ceramic (LTCC) technology can be applied in numerous functions due to a wide variety of benefits, particularly related to flexibility of applications. Controlling the LTCC shrinkage tolerances in the x, y, and z dimensions is critical during manufacturing and avoids an assortment of down-stream issues that will affect yields. All manufacturers of LTCC tape provide a Certificate of Analysis (COA), which contains the results of the manufacturer's shrinkage testing so production variation can be established from lot to lot. Data from this COA is generally used as a starting point in the shrinkage predictions for manufacturing purposes; however, verification of this data must be performed prior to initiating an LTCC build. This paper investigates validation of one manufacturer's COA data and explains how shrinkage differences can occur between the COA data and the data collected during the verification process. The tracking of this data is also presented as a means to ensure proper controls are in place, and the type and style of lamination and cofiring are shown to be significant contributors to these differences. Data will then be presented in association with characterization prior to and after relocation of LTCC fabrication equipment. Additionally, the COA data can be incorporated into shrinkage estimates that will be utilized to set up process parameters, tolerances, and a control plan.

Influence of co-firing process condition on low temperature co-fired ceramics membrane deflection

Purpose – The paper aims to present the influence of the co-firing process conditions of low temperature co-fired ceramics (LTCC) on the deformation of thin LTCC membranes. Design/methodology/approach – The statistical design of the experiment methodology was used in the frame of these investigations to reduce the time and costs of the experiments and to ensure easier interpretation of the obtained results. Moreover, this conception permits the rough estimation of the membrane deflection fired at optimal process conditions. Findings – The applied design of the experiment methodology allowed the researchers to find the optimal co-firing process conditions and to estimate the membrane deflection at the optimal process conditions. The estimation fits well with the results of real measurement that was conducted to confirm the estimation precision. Research limitations/implications – The experiment was conducted for only one type of LTCC, DP951. The precision of the design of the experiment optimization and estimation of the response at optimal conditions depend on the described object. Therefore, the findings of this paper do not have to be generally true for other LTCC tapes, and if other LTCC tapes deformation should be investigated, then similar analysis shall be conducted for them. Practical implications – The deformation of LTCC membranes affects the sensitivity and repeatability of LTCC acceleration and pressure sensors. Hence, the decrease of membrane deflection increases the usability of LTCC in such applications. Originality/value – This paper presents simple optimization of co-firing process conditions of LTCC devices using statistical design of the experiment.

Thermoelectric energy harvester fabricated in thick-film/LTCC technology

Purpose – The purpose of this work was fabrication of a small energy harvester. Design/methodology/approach – The multilayer thermoelectric power generator based on thick-film and low temperature co-fired ceramic (LTCC) technology was fabricated. Precise paths printing method was used to fabricate Ag/Ni and Ag/PdAg thermocouples on a number of unfired LTCC tapes. The tapes were put together to form a multilayer stack. The via holes were used to make the electrical connections between adjacent layers. Finally, the multilayer stack was fired in the appropriate thermal profile. Findings – It consists of 450 thermocouples and generates output voltage of about 0.45 V and output electrical power of about 0.13 mW when a temperature difference along the structure is 135°C. In the paper, individual stages of energy harvester fabrication process as well as its output parameters are presented. Originality/value – Miniaturized thermoelectric energy harvester based on thick-film and LTCC technology was fabricated. As materials, metal-based pastes were used. This is the first paper where multilayer thermoelectric harvester, fabricated with the aid of LTCC technology, was described.

Experimental determination of the uniaxial viscosity of low-temperature co-fired ceramic tapes by vertical sintering

This paper reports the experimental determination of the uniaxial viscosity for ceramic tapes made of three commercially available low-temperature cofired ceramic (LTCC), DuPont 951 (glass–ceramic), Ferro A6M (glass) and Yinfeng 8.5 (glass) by utilizing a novel vertical sintering in an optical dilatometer. The green tapes were vertically sintered at different isothermal temperatures ranging from 760°C to 820°C under their own weights. The densification behavior was systematically investigated through the measured sintering strains and the uniaxial viscosity was determined as a function of relative density based on a theoretical equation developed for ceramic tapes. The calculated uniaxial viscosities were compared with a previously reported model and good agreements were achieved. The activation energy for the uniaxial viscosity was found to be independent of the relative density and showed an average value of 290±47kJ/mol for the DuPont tapes but was not accessible currently for the other glass-based LTCC tapes.

A Biocompatible Low Temperature Co‐fired Ceramic Substrate for Biosensors

Low temperature co‐fired ceramics (LTCC) are widely utilized in the fabrication of compact, three dimensional, and highly integrated microelectronic components. Typical applications include military and mobile electronics applications requiring custom, hermetic, and/or high reliability packaging. These characteristics make LTCC attractive for use in microfluidic and biomedical application. However, commercial LTCC systems are not designed for biomedical applications and have unknown cytocompatibility. In the current work, an LTCC tape has been developed starting with materials of known composition and biocompatibility, a commercially available lime silicate glass and alumina. Tapes achieve high density for sintering temperatures compatible with LTCC processing (850 < T < 1000°C). The LTCC also exhibits low dielectric constant (K = 9.3) and dielectric loss (tan d < 0.005). A commercial gold electrode paste has also been co‐fired with the LTCC, with no delamination, cracks nor camber observed. In vitro biocompatibility was subsequently evaluated using human umbilical vein endothelial cells (HUVECs). HUVECs are observed to attach and spread on fibronectin‐coated LTCC substrates, and also in the leachate obtained by soaking LTCC in cell medium for 7 days. These results establish that the developed LTCC material is biocompatible and suitable for in vitro applications utilizing live cells.

OPTIMIZATION OF SHRINKAGE AND SURFACE-ROUGHNESS OF LTCC TAPE

The Low Temperature Co-fired Ceramics (LTCC) proces s is very popular in the electronics packaging indu stry and is broadly accepted for its low cost and rapid throughput. A m ultilayer LTCC 3-D structure generally shrinks duri ng low temperature co-firing process. Shrinkage occurs in all three dimensions X , Y and Z. Shrinkage has added a challenge to get h igh performance with low temperature co-fired ceramics designs and limited t he yields of LTCC modules, components, subsystems aRoughness is the measure of texture of surface of LTCC tape and a qu antitative analysis of vertical deviation of real surface from its ideal form. This paper describes variations in X, Y and Z direc tions of LTCC tape during firing at different tempe ratures and also describes about the surface roughness of LTCC tape. Data has been con the experimental results and observa tions.

Design and fabrication of a valveless micropump based on low temperature co-fired ceramic tape technology

Low temperature co-fired ceramic (LTCC) tape technology has been widely studied in microsystems and microfluidic devices. The current study presented the manufacturing process of a simple and inexpensive micropump which is made of LTCC. The components of micropump including fluidic channels, diaphragm, chamber, and planar diffuser valves were integrated in one LTCC module. Geometries of these components were designed based on numerical analysis. The finite element analysis was used to characterize the displacement of a piezoelectric actuator and the computational fluid dynamics was applied to design the diffuser. The performance of the micropump was optimized and performance of the designed micropump was carefully examined in the experiments. The data revealed that the performance of a micropump can be significantly increased by adding a pair of pockets. Overall, the study demonstrated that LTCC tape technology is a simple and reliable method to fabricate a valveless micropump.

Characterization of LTCC Tapes in Water Presence

A large number of research have been realized related to investigation of properties of Low Temperature Co-Fired Ceramic (LTCC) materials, such as influence of geometrical parameters, mechanical, electrical, thermal properties, etc. It is well known that ceramic is considered for a material which is impenetrable for water and because of that LTCC is desired for applications in harsh operating environments, such as water. This paper is dealing with investigation regarding the behavior of the LTCC material in water presence. In order to investigate that, an interdigital capacitor (IDC) was embedded between four, six and eight LTCC tapes, positioning IDC always in the middle of the entire structure. Investigation was conducted on two types of LTCC tapes, Heraeus AHT 01-005 and Heraeus AHT 08-047. Influence of the number of substrate layers on overall capacitance of IDC has also been analyzed. Value of capacitance obtained from software was compared with measured capacitance value of fabricated IDC and good agreement was obtained. Appearance of the fabricated structures is shown and measurement results are given.

A 79-GHz LTCC Patch Array Antenna Using a Laminated Waveguide-Based Vertical Parallel Feed

A microstrip patch array antenna based on a low-temperature co-fired ceramics (LTCC) technology is presented in this letter. The antenna is designed for the 77-81-GHz radar frequency band and uses a high-permittivity material (er = 7.3). A laminated waveguide (LWG) was chosen as transmission line, which minimizes coupling and enables the design of LWG-based vertical power dividers. Three stages of power dividers were combined to realize a vertical parallel feeding network. With this feeding-network, the radiation pattern of the proposed antenna is nearly constant across the whole 4-GHz bandwidth. A uniform aperture distribution was chosen. In total, 12 layers of LTCC tapes were used. The measured half-power beamwidth in the E-plane is ≤ 7° across the whole working frequency bandwidth. This compact LTCC antenna (28.3 × 1.2 mm2) is suitable for short/middle-range radar applications, especially for those with a small channel spacing requirement .

Flexography Printing of Silver Tracks on LTCC Tapes – Effect of Printing Direction on Line Properties

The originality of this work is to print with flexography process conductive silver lines suitable for Low Temperature Co-fired Ceramics (LTCC) multilayer systems. Screen printing conductive paste with 65% silver flake particles was optimised for flexography process. Patterns with different line widths – from 100 to 600 μm – were printed in two directions, parallel and perpendicular to printing orientation. Printed lines withstood temperature as high as 875°C for one hour, relative to conventional sintering profile of LTCC multilayer systems. Line width, thickness and roughness decreased after sintering. A minimum line width of 153 μm was measured on sintered lines. Line thickness varied from 1.8 to 3.8 μm and line roughness from 0.7 to 0.9 μm after sintering. Conductive silver lines along 34 cm length were accomplished after sintering. Very low values of electrical resistivity were measured on the sintered lines. This study demonstrates the huge potential of flexography printing for LTCC multilayer systems.

Embedded Ferrite LTCC Inductors

This paper presents for the first time one realization of simple planar inductor realized inside the stack of ferrite LTCC (Low Temperature Co-fired Ceramic) tapes. Presented inductor is one layer square spiral fabricated in the LTCC technology. In order to point out benefits of implementation of ferrite material on inductor inductance, the same inductor geometry was fabricated between two dielectric LTCC tapes. Commercially available LTCC material (both ferrite and dielectric) were implemented for the realization of proposed inductors. Designed structures were characterized and obtained experimental results show that even implementation of a very thin layer of ferrite material around inductor lines drastically increases its inductance. For the same inductor design that occupies the same chip area the inductance enhancement over 11 times is achieved. In addition this enhancement is followed with maintenance of good performance of the inductor.

Biocompatibility Evaluation of Human Umbilical Vein Endothelial Cells Directly onto Low-Temperature Co-fired Ceramic Materials for Microfluidic Applications

Expansion of Low-Temperature Co-fired Ceramic materials into microfluidic systems technology has many beneficial applications due to their ability to combine complex three dimensional structures with optical, fluidic, electrical functions. Evaluations of the biocompatibility of these Low-Temperature Co-fired Ceramic materials are vital for expanding into biomedical research. The few biocompatibility studies on Low-Temperature Co-fired Ceramics generally show negative cellular response to thick film pastes used in generating the electronic circuitry patterns. In this study, biocompatibility of Human Umbilical Vein Endothelial Cells was examined on Heraeus's Low-Temperature Co-fired Ceramic tape and two of their conductive pastes. The biocompatibility was assessed by monitoring cellular attachment and viability up to three days. This study examines the idea of leachates being detrimental to cells due to a study that suggests the possibility of harmful leachates. Results indicate difficulty in initial attachment of Human Umbilical Vein Endothelial Cells to sintered Low-Temperature Co-fired Ceramic tapes, but no hindrance of cellular attachment and growth onto the two conductive pastes. Outcomes also demonstrate that possible harmful leachates from Low-Temperature Co-fired Ceramic materials don't thwart cellular attachment and growth for up to three days of cell culturing. These results provide a basis for biological devices using Low-Temperature Co-fired Ceramic materials.

The Effect of Phase Composition on the Mechanical and Thermal Properties of LTCC Material

Low-temperature co-fired ceramic (LTCC) is an important material in the production of ceramic multilayer structures. Large and complex multilayer structures are usually fired at higher temperatures and/or longer firing times compared to the relatively thin LTCC tapes. The firing conditions of LTCC determine the phase composition and the microstructure, which both influence the physical characteristics, such as the mechanical and thermal properties. In this work the effect of the phase composition on the biaxial flexural strength and the temperature coefficient of expansion of the DuPont 951 LTCC is presented. The samples were fired at different temperatures and times to obtain different phase compositions. The phase composition, especially the mass fraction of anorthite, was correlated with the biaxial flexural strength and the thermal coefficient of expansion (TCE). A very long firing time, i.e., 100h at 800 °C, yields, apart from crystalline anorthite, the cristobalite phase. The anorthite that crystalizes from the glass phase in a dense LTCC material changes the crack-propagation mechanism and improves the biaxial flexural strength of the material. The major change in the biaxial flexural strength is observed when the anorthite phase appeared. The increasing mass fraction of anorthite does improve the biaxial flexural strength less drastically. With the increasing mass fraction of the anorthite, decreases of the TCE of the material and a small decrease of the density of the LTCC material occur.

Magnetic DC-Properties of LTCC-Ferrite Material and Their Temperature Dependence

Low temperature co-fired ceramic (LTCC) technology allows to create 3-D ceramic devices from tapes with different electrical and magnetic properties. Recently ferrimagnetic materials became available as LTCC tapes. To magnetically characterise the ferritic LTCC material we have realised ring samples using ESL 40012 LTCC-tapes. The ring core fabrication process and the sample preparation are described in detail. The quasi-static B(H) curve has been measured by inductive methods, and its dependence on temperature between room temperature and the Curie temperature is shown.

Complex Permeability Changes of Ferritic LTCC Samples With Variation of Sintering Temperatures

The complex permeability of commercially available ferrite LTCC (Low Temperature Cofired Ceramics) tapes in dependence of peak sintering temperature have been measured and calculated in the high-frequency range (300 kHz-1.2 GHz). For the first time this dependence is determine at five peak sintering temperatures up to 1300°C. Permeability values have been calculated from S-parameters measured with a vector network analyzer and a short ended coaxial sample holder into which ferritic LTCC toroids have been placed. The toroids were realized by stacking and laminating 62 layers of green tape and then sintered at peak temperatures of 885°C, 1000° C, 1100°C, 1200°C and 1300°C, respectively. Obtained complex permeability values for these toroidal LTCC samples are presented. The maximum real part of permeability values increase up to 930 (at 1100°C firing peak temperature) and show a shift to lower frequency values. At higher sintering temperatures (1200° C and 1300°C) real part of permeability of ferrite samples starts to decrease with further shifting to lower frequency values. In order to determine variation of grain size caused with increasing of sintering temperature and its influence on material complex permeability, an microscopic inspection of samples was performed. Also, using the model of the complex permeability spectra, dispersion parameters of ferrite LTCC material has been determined for various sintering temperatures.

Application of Design of the Experiment in Preliminary Investigations on the end Milling of Low Temperature Co-fired Ceramics

The formation of three-dimensional shapes is one of the most important technological steps in low temperature co-fired ceramics (LTCC) process. Channels and chambers qualities and the process speed are strongly affected by the shaping procedure. There are three main machining techniques: laser cutting, punching, and milling. This article is dedicated to end milling process of LTCC tapes. The determined PS/DK 23 experiment design was used in the investigations and its procedure is described in this article. The used procedure is a very flexible method to achieve much useful information about the influence of the process parameters on the output. The PS/DK 23 experiment design enables analysis of the influence of: the three input parameters on the output (minimal obtained feature) and the interaction between the input parameters on the output (minimal obtained feature). Moreover, PS/DK 23 experiment design enables to obtain the mathematical model of the milling process and to decrease the number of measurements demanded to achieve the correct model. Hence, the design is suitable to decrease the time and costs of the experiment. The influence of the following input parameters: spindle rotational speed, spindle feed rate, vertical spindle step, and cutter diameter on minimal obtained feature of LTCC tapes is analyzed in this article.

Sintering Behavior, Properties, and Applications of Co‐Fired Piezoelectric/Low Temperature Co‐Fired Ceramic (PZT‐SKN/LTCC) Multilayer Ceramics

Materials and processing conditions have been developed allowing co‐firing of fluxed PZT‐SKN materials with commercial low temperature co‐fired ceramic (LTCC) tapes. Previously, Pb(Zr0.53, Ti0.47)O3–Sr(K0.25, Nb0.75)O3 (PZT‐SKN) ceramics fluxed with 1 wt% LiBiO2 and 1 wt% CuO addition were shown to sinter to high density at 900°C for 1 h, with a large d33 piezoelectric coefficient of ~415 pm/V. Currently, the master sintering curve (MSC) approach has been used to study the densification behaviors of fluxed PZT‐SKN and LTCC tapes. Different sintering mechanisms for fluxed PZT‐SKN ceramics and LTCC materials are confirmed by analyzing the apparent activation energy (Qa). Using knowledge gained from MSC results, an optimized sintering profile was developed. Multilayer PZT‐SKN/HL2000 (HeraLock™ Tape, Heraeus) stacks co‐fired at 900°C for 0.5 h maintain large piezoelectric coefficient (high field d33 > 340 pm/V). EDS analysis reveal limited interdiffusion of Pb from PZT‐SKN layers in LTCC and the appearance of Al, Ca, and Si in the PZT‐SKN near the PZT‐SKN/LTCC interface. Further, elemental interdiffusion was not detected at the center of piezoelectric layer in PZT‐SKN/LTCC multilayer ceramics and no subsequent reduction in piezoelectric coefficient d33 was observed. Finally, a piezoelectric microbalance with mass sensitivity of 150 kHz/mg was fabricated using the materials and methods developed.

Fabrication of an Inductively Coupled Plasma Antenna in Low Temperature Co‐Fired Ceramic

A miniature electrostatic thruster is being developed in Low Temperature Co‐fired Ceramic (LTCC) at Boise State University. The thruster is composed of an antenna to create the plasma, a cylinder to contain the plasma, and grids to extract the plasma beam at high velocity. In this work, the development of the inductively coupled plasma (ICP) antenna in LTCC will be presented. This antenna is fabricated using DuPont 951 LTCC tape. A Direct Write dispenser is used to apply silver paste for the spiral ICP antenna. Using LTCC allows for the antenna to be embedded in the device under a thin sheet of LTCC dielectric, which protects the antenna from ion back bombardment during operation. This thin sheet is the seventh layer of the total device, with the ICP antenna one layer below the top. The design of the antenna is based on the research done by J. Hopwood. This article discusses the fabrication and performance of the ICP antennas in LTCC. These ICP antennas are operated at pressures from 10 mTorr to 1 Torr with radio frequencies (RF) of 500 MHz to 1 GHz to inductively couple with low‐pressure argon to produce plasma. The performance of the antennas will be verified with data showing the start and stop power of the plasma at various pressures and an electric field map of the RF field above the antenna.

Microforming process for embossing of LTCC tapes

Embossing of low-temperature cofired ceramics (LTCC) enables the fine patterning of these multilayer materials in the green state and thus allows the fabrication of smart ceramic microsystems even for moderate quantities or prototypes. To understand the embossing process, mechanical properties such as the viscoelastic modulus, yield strain and densification are investigated for commercially available LTCC tapes. The forming and shrinkage behaviour are compared for large cavities as well as for fine patterns. The results are discussed and a comprehensive explanation of the forming mechanism is worked out. Relevant material properties are identified and the microforming of different tapes is explained under consideration of their mechanical properties. This paper therefore gives an essential guide to understanding the main forming influences and failures for LTCC tapes.